The rising tide of human pathogens that are resistant to antibiotics has created an urgent need for new treatments for serious bacterial infections. Novel approaches that circumvent traditional mechanisms of antibiotic resistance, can be effective against biofilms, and avoid disruption of the native gut flora are especially desirable. This clinical challenge has sparked renewed interest in bacteriophage (phage) therapy. Demonstration of efficacy in an animal model of infection is a preliminary step in the development of a new therapeutic agent.